The area covered by sea ice hovered near its historic low this summer. In Greenland, record-high temperatures this year have helped accelerate the melting of the country’s massive ice sheet. Throughout the Arctic, permafrost is warming and the blanket of snow is shrinking. Those changes appear to be long-lasting, said an international team of climate experts who wrote the National Oceanic and Atmospheric Administration report. [...] “The Arctic is a system, and the system is changing,” said Don Perovich, a sea ice expert with the U.S. Army Corps of Engineers who worked on the report. “It’s not just that sea ice is being reduced. There’s changes in Greenland, the atmosphere, the ecosystem, and these changes are affecting human activity.”

What is increasingly apparent, as researchers have warned for years, is that “polar amplification” is causing many of these changes to feed on themselves, amplifying each other year after year. In this regard, what is happening to Arctic sea ice is in many ways key.

As the National Snow and Ice Data Center (NSIDC) pointed out earlier this month, Arctic sea ice is not just diminishing in extent — the four lowest levels have been in the last four years — but it is also younger and thinner. That makes ice easier to melt each year, which in turn exposes greater areas of heat-trapping ocean, which causes further melting, making it more and more difficult for sea ice to recover to previous levels.

Among other impacts, such changes in sea ice cover could have significant and seemingly contradictory impacts on weather patterns in mid-latitudes. Rising heat from a warmer Arctic may increasingly disrupt the circumpolar winds that normally confine cold air within Arctic realms, allowing blasts of cold to hurtle south, similar to what happened when parts of the United States were buried under thick snow this past winter.

“While individual weather extreme events cannot be directly linked to larger scale climate changes, recent data analysis and modeling suggest a link between loss of sea ice and a shift to an increased impact from the Arctic on mid-latitude climate,” concludes the report. “With future loss of sea ice, such conditions as winter 2009-2010 could happen more often. Thus we have a potential climate change paradox. Rather than a general warming everywhere, the loss of sea ice and a warmer Arctic can increase the impact of the Arctic on lower latitudes, bringing colder weather to southern locations.”